png::image is a C++ class for creating, reading, and writing PNG image files. It provides direct RGBA pixel access and basic image manipulation with minimal external dependencies.
- Linux
- zlib is required to support cyclic redundancy check (CRC) operations used by the PNG format for checksum generation and validation.
The configure script generates a Makefile. The installation prefix specifies the destination directory and defaults to /usr/local.
./configure --prefix=/usr/localBuild the static library:
makeThis produces the libpngimg.a archive.
To install the library and header files:
make installInstallation deploys:
${prefix}/lib/libpngimg.a${prefix}/include/pngimg.hpp
After installation, you can run the test suite, which generates sample images in the test/ directory:
make testpng::image supports reading from existing files and creating new images. Pixel access is performed via operator[], providing row-based access to pixels in RGBA form with channel values in the range 0–255. Both 8-bit and 16-bit bit depths are supported; conversion behavior depends on configured bit depth.
Operations may fail (e.g., loading or saving files) and will print error messages to the terminal. Users should check for success where appropriate.
#include <pngimg.hpp>
void createFile()
{
png::image img;
// Configure File
img.setColorType(png::ColorType::TRUECOLOR_ALPHA);
img.setBitDepth(png::BitDepth::BIT_16);
// Set a square of 10x10 pixels to orange
for (int x = 0; x < 10; ++x)
for (int y = 0; y < 10; ++y)
img[x][y] = png::rgba(255, 127, 0, 255);
// Save the file
if (img.save("/path/to/newfile.png"))
std::cout << "Saved the file" << std::endl;
}
void adjustFile()
{
png::image img;
// Load the file
if (!img.load("/path/to/file.png"))
return ;
// Set a square of 10x10 pixels to orange
for (int x = 0; x < 10; ++x)
for (int y = 0; y < 10; ++y)
img[x][y] = png::rgba(255, 127, 0, 255);
// Save the file
if (img.save("/path/to/file.png"))
std::cout << "Saved the file" << std::endl;
}Compile and link against the PNG library and zlib:
g++ main.cpp -lpngimg -lzIf the library is not installed in a default system location, specify the include and library search paths explicitly:
g++ main.cpp -I${prefix}/include -L${prefix}/lib -lpngimg -lzA PNG file starts with a default sginature {0x89, 'P', 'N', 'G', '\r', '\n', 0x1A, '\n'} followed by a sequence of data chunks. A few chunks are critical (IHDR IDAT IEND), whereas the rest is optional, and many chunks have a specific order in which they appear.
| Bytes | Field | Description |
|---|---|---|
| 4 | Chunk Size | Length of the chunk data in bytes (big-endian) |
| 4 | Chunk Type | 4-letter name of the chunk type (e.g., IHDR, IDAT, IEND) |
| n | Chunk Data | The actual data of the chunk. Its length is specified in Chunk Size is thereby capped at 2^32 - 1 bytes (4,294,967,295) |
| 4 | CRC | Cyclic redundancy check for the chunk type and data, used to ensure data integrity |
The IHDR chunk specifies the Color Type and Bit Depth of the PNG image.
Color Type determines how many channels each pixel uses and what those channels represent. It can specify black-and-white (GRAYSCALE) or full-color (TRUECOLOR) images, with the option to include a transparency channel (ALPHA). Alternatively, a palette-based (PALETTE) color type uses a single channel whose values index into the PLTE chunk.
For converting a color image to grayscale, the luminance Y is calculated as a weighted average of RGB:
| Channel ↓ \ ColorType → | GRAYSCALE | GRAYSCALE_ALPHA | TRUECOLOR | TRUECOLOR_ALPHA |
|---|---|---|---|---|
| 0 | Y (R,G,B) | Y (R,G,B) | R | R |
| 1 | — | A | G | G |
| 2 | — | — | B | B |
| 3 | — | — | — | A |
Bit Depth dictates the number of bits per channel, defining the range of values each channel can store. The most common depth, 8 bits (1 byte), allows the standard RGB range of 0–255.
https://www.libpng.org/pub/png/spec/1.2/PNG-Structure.html
https://medium.com/@0xwan/png-structure-for-beginner-8363ce2a9f73
https://www.w3.org/TR/PNG-Chunks.html
https://framebird.io/exif-metadata-viewer/png
https://pics.io/photo-metadata-viewer
Othello
Copyright (c) 2026 Othello
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The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
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Any use of the Software in a public project, website, application, or distributed product must include clear attribution to the author (Othello), such as in a credits file, documentation, or an “About” section.
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xxd image.pngcustom install
make clean && ./configure --prefix=$HOME/.local && make && make install && make testecho "$PATH" | sed -e 's/:/:\n/g' -e "s#$HOME#\$HOME#g" | sortmake clean && ./configure --prefix=$HOME/.local && make && make install
./configure --prefix=$HOME/.local
make
make installc++ -v -E - < /dev/null 2>&1 | sed -n '/#include <...> search starts here:/,/End of search list./p'g++ -print-search-dirs | sed -e 's/:/:\n/g' | sort